Agricultural combines harvest an agricultural crop, thresh the harvested crop to break the large crop components from the smaller crop components, separate the smaller crop components from the larger crop components, and clean the smaller components to eliminate chaff from the grain. The combine may be equipped with various harvesting assemblies including grain platforms (rigid and flexible), corn headers, row crop headers or windrow pickup platforms depending on the crop and the harvesting practices employed by the farmer. Similarly, the threshing assembly of the combine may be configured in a number of different ways, including a conventional transverse threshing cylinder and concave, or a rotary threshing system that is either axially of transversely arranged. In addition, the separating assembly may comprise conventional straw walkers or rotary assemblies.
The cleaning system removes chaff from the grain. The cleaning system typically comprises a cleaning shoe and a cleaning fan. The smaller crop components from the threshing assembly and the separating assembly are directed to the cleaning shoe. The cleaning shoe typically is provided with a chaffer and a sieve. The chaffer and sieve have transverse louvers that define openings. The heavier clean grain falls through the openings formed by the louvers on the chaffer and the sieve. The air blast from the cleaning fan blows the chaff out the rear of the combine.
There are three types of cleaning shoe actions, they are: reciprocating, shaker and cascading. In a reciprocating shoe the chaffer and sieve move in opposite directions to one another. In a shaker shoe the chaffer and sieve move in the same direction at the same time. In a cascading shoe the chaffers and sieve are positioned so that the small components drop from one unit to another in a cascading or rolling motion.